I use Photoshop CS5 for mac (click here for Photoshop CS5 for PC) & Screenium .
Step 1: Select the part of the video you want to gif
Obviously you need to know WHAT you want to gif before you can start making your gif. Open your video and set it to start playing right before the part you want to gif
Step 2: Record the bit you want to gif
Open screenium (or any other program you might be using) and set it to fixed area, like so:
and select the area (youtube page, Quicktime player, etc) you want to record, like so
Press record and start your clip. When you got what you wanted, you can press cntrl + alt + c to stop recording and stop your video. Once you've gotten the part, you can export it
Step 3: Import the clip into photoshop
Now you have to open the clip in photoshop so you can start giffing it. Go to File --> Import --> Video frames to layers.
Then select "Selected range only" and tick the "Limit to ever...frames" box. I usually do limit to every 4 frames if it's a longer clip, and 2 or 3 if it's a shorter clip. This way it's not importing every frame from the clip, but only every 4th frame, so you don't get a shitload of frames. Then press play to select the part you want to gif.
Now you've imported the clip into photoshop, your photoshop screen should look something like this:
You always want to try and keep your gif under 15 frames, or it will be too big to upload onto Tumblr. Here you can delete any frames you might not need. Maybe you started the clip too soon and you can delete the first or last couple of frames, or you can try and delete a few frames here and there to shorten the gif.
Now that you've gotten your gif down to 15 or less frames, you want to resize it. The best size to use on Tumblr is 500 px wide. Any wider, and Tumblr won't let you upload it, any smaller, and people will hate it. Just go to Image --> image size and change the image width to 500 px.
Now you might want to change the speed of your gif. Just select all your frames, click on one of them and the following window should pop up
I usually do mine at 0.12 seconds or 0.15 seconds (you can select this by selecting "other" at the bottom of the window)
To save your gif, you go to File-->save for web and devices, make sure it's under 500KB, and press OK!
TADAAA, YOUR GIF IS NOW FINISHED
Please keep in mind that this is my first ever tutorial. My next tutorial will be on reducing the size of your gif & adding effects and stuff.
Please know that if you ask any questions about gif making on ANON, they will NOT be answered.